Log Message:
games/7kaa: build even when CFLAGS has -Werror=char-subscripts

The upstream code looks very suspicious.  It forces compilation with
-fsigned-char and then uses signed characters to index a 256-entry table,
for example in IMGbltAreaRemap.  But only in the C++ code.
The corresponding assembler code uses unsigned bytes.
I'll let them fix this bug themselves.